This invention relates to a surgical instrument which has an actuating trigger or lever to perform a desired function. More specifically, it relates to such an instrument which requires the user to squeeze or depress a trigger or lever with the hand to operate the instrument to perform a desired function.
Surgical instruments routinely incorporate a frame which houses a pistol grip trigger or lever. When the user squeezes the trigger, or depresses the lever, an "end effector" at the business end of the instrument is actuated to perform a desired surgical function. For example, the end effector may cause bodily tissue to be clamped, cut, fastened with staples, or all three of these.
A surgical instrument which has found widespread acceptance and use is the linear cutter, sometimes referred to as the endocutter when adapted for endoscopic surgical applications. A surgical cutter includes an end effector having opposed jaws movable relative to each other, one jaw containing an anvil and the other containing a cartridge housing a plurality of staples. Tissue is clamped between the jaws, and then staples are fired into the clamped tissue to fasten the tissue. As the staples are fired, a knife cuts the tissue between the vertical rows of staple lines. The end effector of a surgical cutter is actuated to perform these functions when a first trigger or lever is squeezed or depressed to clamp the tissue between the opposed jaws, and then a second trigger or lever is squeezed or depressed to fasten the tissue with staples and cut the tissue between the staple lines.
Of course, other surgical instruments having end effectors performing other functions are used or have been described for use in various medical and surgical procedures. These other instruments also require an actuating trigger or lever to manipulate the end effector.
When the trigger or lever of a surgical instrument is actuated to manipulate the end effector for performing a desired function, the user must apply force to cause the actuation by squeezing the trigger or depressing the lever against the frame of the instrument. The amount of force which the user must apply depends on whether the instrument can efficiently transfer that force from the frame to the end effector, and also on the particular function which the end effector is intended to carry out. Often, it may be difficult to transfer the force applied from the frame of the instrument to the end effector when the instrument is particularly adapted for endoscopic surgery. An endoscopic instrument typically has an elongated, small diameter shaft between the frame and the end effector. Therefore, the force applied when the trigger or lever is actuated must be transferred into and through the elongated shaft to the end effector, and this can sometimes result in undesired inefficiencies. In addition, the clamping of tissue and the firing of staples into tissue also requires the delivery of high forces to the end effector. As the thickness of the tissue increases, the amount of force necessary to clamp and fasten tissue likewise increases.
In some situations, particularly those involving the use of endoscopic cutters to clamp, fasten and cut tissue, the forces generated when the user squeezes the trigger or depresses the lever to perform these functions may be excessive. In other words, the forces generated to manipulate the end effector in a desired way under certain "loading" conditions may exceed the design specifications of one or more of the various components of the instrument. Unfortunately, when this occurs, those components for which the design specifications have been exceeded may break. Consequently, the instrument fails for its intended purpose. Not only can this occurrence be simply troublesome and inconvenient because the surgeon unexpectedly needs to replace the broken instrument with a working one, but also potentially dangerous. The surgery may have proceeded to a particularly delicate point where easy replacement of the instrument is impractical, or the tissue may have been damaged because it was inadvertently manipulated in an improper way.
Actuating mechanisms have been described which have not fully addressed the situation which may arise in surgery where excessive forces are encountered. Co-pending application Ser. No. 08/235,070, filed Apr. 29, 1994, describes an endoscopic surgical cutter which includes a clamping trigger on a pistol grip handle. If tissue beyond a preset range of thickness is inserted between the jaws for clamping, the clamping trigger will not latch into its fully actuated position when the handle is squeezed. Instead, the latch mechanism cannot be activated, and the clamping trigger will return to its normal unactuated position to prevent the user from firing staples into the tissue. However, if excessively thick tissue is placed between the jaws, then it is still possible for the user to apply undue force to the clamping trigger resulting in a failure of one or more parts of the instrument.
Since the surgical instruments currently available in commerce or described in the literature do not fully address the potential for applying excessive force to an actuating trigger or lever of the instrument to cause an instrument failure, a mechanism which prevents the application of excessive force to prevent damage to the instrument, and more importantly, to the patient, is highly desirable.